1. Field of the Invention:
This invention relates to a new and improved boiler and particularly to a boiler composed of an elongated generally rectangular hollow slab wound about a horizontal axis to define internally a body for holding a heat exchange medium therein, and externally defining a firebox and an exhaust gas passage between adjacent convolutions, leading the products of combustion from the firebox to an exhaust stack. The term "boiler" is not used in any limiting sense, but includes any fluid heater, such as is often referred to as a steam or hot water boiler, or furnace, in which the fluid is heated by burning fuel and by the hot products of combustion.
One of the particular objects of this invention is to provide a boiler in which the firebox is arranged to be surrounded on the sides by the heat exchange medium, and heat exchange medium flow occurs with controlled velocity and in a direction countercurrent to combustion gases.
Another object is to provide a boiler in which the velocity and direction of combustion gases may be controlled countercurrent to heat exchange medium.
A further object is to provide a boiler with a minimum external surface exposed to high temperature products of combustion.
A still further object is to provide external surfaces of a boiler cooled by the lowest temperature level of heat exchange medium.
Another object is to minimize the volume of heat exchange medium residing in the boiler.
The arrangement of a boiler in the configuration described renders particularly effective heat transfer, is suited to intermittent operation common to many boiler applications and has other novel advantages which will be apparent from the following description. 2. Prior Art:
It is known to form boilers out of tubular members wound in a plurality of convolutions to define a firebox and products of combustion passage. The helix so formed is usually disposed about a vertical axis. The circulation of heat exchange media, such as water, may be drastically attenuated by reason of the excessive length of the coils. Flow of products of combustion relative to heat exchange media is difficult to control, and are not truly counter to each other, thus heat transfer is not at maximum efficiency.
The volume of heat exchange medium in the boiler may be very large, and excessive energy may be consumed in causing the medium to traverse the long tube length.
In addition, horizontal boilers of the "Scotch Marine" type are well known in the art. Flow of products of combustion is generally through round tubes, frequently with turbulence inducers inserted to improve heat transfer. Efforts have also been made to improve heat transfer by making oval tubes to increase heat transfer area in relation to inside cross section area of the tubes. While these improvements have increased the efficiency of the performance of this type boiler, on the products of combustion, yet water flow remains generally uncontrolled, and not counter to products of combustion flow.
While the firebox is contained internally within the boiler, the inside of large exterior surfaces are frequently exposed to high temperatures of the products of combustion. In addition, exchange medium backed external surfaces are exposed to temperatures at or close to highest temperature attained in the boiler for this fluid. The combination permits considerable surface heat losses to occur.
While the "Scotch Marine" or similar designs are generally considered to have small water storage, the volume in reality is quite large and retains considerable unusable energy on each shutdown in intermittent service which frequently is lost during the standby cycle, through room air flow into the firebox, through the boiler and up the exhaust stack taking with it heat from the boiler inner surfaces as well as external heat loss from outside surfaces to the room.